How to Wire a 3 Phase Air Compressor

By Dave Rongey - Summary:

Wiring a 3 Phase Motor for an Air Compressor: The Basic Requirements for Wiring Electric Motors, 3 Phase Motor Circuits

Air Compressor Electric Motor

Electrical Question: We have a Saylor Beall air compressor we are trying to get wired up. It ran fine at the previous shop and then we moved it to this shop. The motor is 3 phase and it appears to be wired according to the diagram for the low voltage 220. The label shows that it can be wired for 220 or 460. It is all wired and hooked up to the controller, but here is where we are having problems, we cant get it to start, it only hums. The motor starter is a Cutler Hammer # A10CNO. The wires from our shop circuit breaker has 2 yellow hot wires at 120 volts each, 1 white neutral wire and 1 green ground wire. Is it possible to wire the compressor with this combination of wires and where do they go? When the compressor was moved it was simply unplugged from the wall and moved, all pressure switches and motor wires are in their same locations as before.

This electrical wiring question came from Cody, in Enid, Oklahoma.

Dave’s Reply:
Thanks for your electrical wiring question Cody.

Wiring a 3 Phase Motor for an Air Compressor

The Basic Requirements for Wiring Electric Motors

Every motor should have a name plate which is typically attached on the side or end of the motor. The information found on the label tells all about the motor size and electrical requirements. To stay on track with this question, the shop where the motor is to be installed must have an electrical service which supplies either 3 phase 230 volts, or 3 phase 460 volts.

Electrical Service Panels

Just like electric motors, an electrical service panel should be equipped with a label which is attached either on the cover or inside the door. The information on this label will be specific to the make and model of the electrical panel along with the voltage and amperage rating. Here in the USA, a typical home electrical panel may be 120/240 volts 125 amps. The actual amperage capacity of the panel is best known by examining the Main Disconnect or Main Circuit Breaker, which will have the amperage rating identified, such as on the breaker handle.

Electrical Power for 3 Phase Motors

Without getting too technical, a 3 phase electrical service panel will produce 3 separate lines of electrical power. A 120/240 volt single phase panel found at a home or shop can only provide up to two separate lines of power, therefore this type of electrical service could not provide the necessary power for a 3 phase motor.

3 Phase Motor Circuits

As described above, a typical 3 phase motor circuit will have 3 separate insulated wire conductors for the power and the ground wire. A neutral wire is not required for a 3 phase motor.

A Summary of Wiring 3 Phase Motors

Identify the required voltage and amperage.

Determine if the electrical service panel has the same voltage and available amperage capacity.

Electric motors are typically wired to a motor controller or motor starter which is sized appropriately to the horsepower of the motor and has thermal overload protection.

House Wiring Circuits and Circuit Breakers

This article looks at common 120 volt and 240 volt house wiring circuits and the circuit breakers that are installed identifying the types and amperage sizes used in most homes.Electrical Panel Circuit Listing

Electrical Wiring and Electrical Repairs

Unless otherwise posted, please refer to the following Guidelines for Electrical Projects:
Skill Level:
Intermediate to Advanced - Electrical Repairs and Circuit Wiring is Best Performed by a Certified Electrician or Licensed Electrical Contractor.
Electrical Tools Required:
Basic Electricians Pouch of Hand Tools, a Voltage Tester and a Multi Meter.
Estimated Time:
Depends on personal level experience, ability to work with tools, work with electrical wiring, and the available access to the project area.
Precaution:
Identify the project circuit, turn it OFF and Tag it with a Note before working with the wiring.
Important:
Modifying existing electrical circuits or installing additional electrical wiring should be done according to local and National Electrical Codes, with a permit and be inspected.